The present invention generally relates to the field of battery chargers, and more specifically to automatic battery chargers.
Charging a storage battery can be a dangerous endeavor. Hydrogen gas generated by the electrolyte of a storage battery can explode if ignited by sparks generated when connecting the terminals of the battery to an energized battery charger. Of course the power switch to the battery charger may be in the off position, however, this requires a conscious effort.
Many battery chargers provide a manual voltage select switch so that one battery charger may be used to charge batteries having different operating voltages. However, battery chargers of this type require the operator to consciously select the appropriate position of the voltage output switch. While this task is relatively simple, it may not always be followed, with the ensuing potential to overcharge the battery or cause it to explode.
Battery chargers are also used to charge the batteries of mobile platforms such as autonomous robots. A specific application of this type of system is where a battery powered robot seeks a battery charging station when a low battery voltage condition is detected by the robot. The automatic charging function of a mobile platform such as a robot can be broken down into two specific subtasks: 1) locating and homing in on the charging station, and 2) making the physical connection between the charging station and the mobile platform. Numerous proposed solutions to accomplish these tasks have been developed. Most employ a favored and sometimes specific direction of approach which significantly complicates the task of alignment and mating, and thus reduces the overall effectiveness of the system.
One standard approach calls for the alignment of a special plug on the robot with a mating receptacle on the charger. This can be done, but requires complicated hardware and software, and thus is susceptible to problems which reduce the system reliability. If the plug is designed to mate with a conventional AC distribution system, electrical shock is introduced as a potential hazard.
Another type of existing system consists of a rectangular platform with a semicircular cavity in one side, and a track tape lying on the floor, extending from the cavity. When the robot detects a low voltage battery condition, it starts searching for the track tape by random motion or by using preprogrammed information about the environment in which it is operating. If it finds the tape, the robot follows it to the charging station, where connection is made with two contacts, one on each side of the cavity. There are several disadvantages to this approach. The robot wastes a lot rapidly diminishing power searching for the tape. The tape itself must be physically installed on the floor, where it is subject to abuse. The charging station cannot easily be relocated without moving the tape and reprogramming the robot with information on where to search unless random searching is employed. The approach path is constrained to a single direction as defined by the tape. Objects which inadvertently block this path can impede a connection. Another problem with this type of system is that if the robot is not perfectly aligned when entering the cavity, a good connection may not be made.
Other approaches involve the use of coded near-infrared beacons for homing. One embodiment involves placing the beacon on a wall behind the charging unit, typically situated on the floor below. Because this is not a self-contained system, errors can arise from any subsequent displacement of the charging unit with respect to the beacon. Such displacement may result from human intervention, as for example, if the charger is moved by a cleaning crew or as a consequence of robot impact during the docking procedure.
One type of system solves this problem by placing the beacon on an enclosure roughly the size of a telephone booth which the robot enters to effect a connection. Spring contacts mate with two circular bands around the robot's base to furnish the charging current. This solution is relatively costly, less flexible in terms of relocation within the operating area, but is obtrusive. In either case, the approach of the robot to the charging station must be made within a narrowly defined window of access. This is a major drawback should the path become obstructed.
In the foregoing examples, it is very difficult for the robot to measure the distance to its charging station using ultrasonic ranging techniques as it approaches, due to problems associated with specular reflection from smooth surfaces. This provides an additional ambiguity by making it difficult for the robot to locate the target charging station.
Another problem common to all systems of this type is contact degradation at the mating surfaces of the robot and charging station due to make-and-break action of the conductors, especially where heavy charge current is employed. This problem is further aggravated due to the mechanical bounce which occurs as a consequence of the impact between the robot and charging station which can cause damaging power transients in the computer logic and control circuitry onboard the robot.
Therefore, one object of the present invention is to provide a battery charging system that may be energized while being connected to a storage battery to be charged, but which automatically delays application of charging current to the battery until after a sufficient time has elapsed to allow the battery terminals to be secured to the battery charging station. Another object of the present invention is to provide a battery charging system that automatically determines the proper voltage to be applied to the battery being charged.
Another object of the present invention is to provide an automatic charging station that will not energize its outputs if the outputs are shorted together. A further object of the present invention is to provide an automatic charging station for charging the battery of a mobile platform that indicates its precise location to the mobile platform. Another object of the present invention is to provide an automatic charging station that has a simple, yet reliable contact configuration. Still another object of the present invention is to provide an automatic charging station that minimizes degradation of the contacts of both the charging station and the mobile platform while the battery of the mobile platform is being charged.